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Charles Messing's Crinoid Pages: Artificial Key to the Families of Living Crinoids

The Sea Lilies and Feather Stars

[NOTE: Ongoing taxonomic revisions will require changes to this key]

1a.  Segmented stalk absent.
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1b.  Segmented stalk present.
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2a. (1a) Crown attached directly to substrate via expanded or stump-like base (figure 1).

Fig. 1. Holopodidae. A. Holopus rangii (from Carpenter, 1884). B. Holopus rangii and small dark Cyathidium pourtalesi (arrows); note pale bluish juvenile H. rangii left of center and upper right that resemble C. pourtalesi.


2b. (1a) Crown attached to substrate via hook-like, prehensile or slender cirri (absent in a few genera) that arise from a single remaining stalk segment, the centrodorsal, which may be discoid, hemispheric, conic or cylindrical (figure 2).
---Go to 16 [Feather stars]

Fig. 2. Feather stars. A. Himerometra robustipinna. B. Sarametra cf. triserialis. C. Phanogenia typica, aboral view showing small centrodorsal lacking cirri.

3a. (1b) Stalk composed of two or (possibly) a few columnals; rays at least weakly asymmetric, arising obliquely from radial circlet.
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3b. (1b) Stalk composed of numerous columnals; crown symmetric, oriented radially on top of stalk.
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4a. (3a) One conic holdfast columnal; calyx elongated, subcylindrical; radials fused; three rays longer and larger than other two; arms coil inward over oral surface; proximal brachials roof ambulacra (figure 3A-B).
---Sclerocrinidae (Neogymnocrinus richeri)

4b. (3a) Known only from a few short subcylindrical or slightly conic calices; short, lower portion a fused cylinder; radials wider and taller with lateral sutures visible, but no clear basal sutures; radial articular faces narrow, the central face much larger than either pair of flanking faces; stalk and arms unknown (figure 3C).
---Eudesicrinidae (Proeudesicrinus lifouensis)


Fig. 3. A-B. Sclerocrinidae, Neogymnocrinus richeri. C. Eudesicrinidae, Proeudesicrinus lifouensis.

5a. (3b) Columnals differentiated into nodals bearing segmented cirri, and internodals lacking cirri, at least on proximal part of column.
---Go to 6Order Isocrinida

5b. (3b) Stalk without cirri; no columnals differentiated as nodals.
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6a. (5a) Rudimentary, cirrus-bearing nodals restricted to proximal part of stalk; cirrus sockets obliterated distally; stalk terminates in a cementation disk; basals form a short, cylindrical circlet; radials form a much larger conic circlet; I and IIBr series of 2 ossicles each (figure 4A).
---Proisocrinidae (Proisocrinus ruberrimus)*

6b. (5a) Stalk composed of cirrus-bearing nodals alternating with series of internodals; basals joined as a low circlet or separated by the radials; IBr and, when present, IIBr series of 1-11 ossicles (figure 4B-C).
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Fig. 4. A. Proisocrinidae, Proisocrinus ruberrimus. B. Cenocrinus asterius. C. Endoxocrinus parrae.

7a. (6b) Primibrachial articulation a synarthry (figure 5).
---Isocrinidae (Neocrinus, Hypalocrinus)*

7b. (6b) Primibrachial articulation a syzygy (figure 5).
---Cainocrinidae (Teliocrinus)*

7c. (6b) Primibrachial articulation a synostosis (figure 5).
---Isselicrinidae (Cenocrinus, Metacrinus, Saracrinus, Endoxocrinus)*

*Classification of crinoids placed in these three families here remains under debate (see, for example, Roux et al. 2009).  For convenience, this key roughly follows Hess (2011). However, molecular data place Proisocrinus as a sister to Hypalocrinus, so it may not rate its own family.


Fig. 5. Arrows indicate articulation in first primibrachial series. (Left) Isocrinidae, Neocrinus decorus, synarthry. (Center) Cainocrinidae, Teliocrinus springeri, syzygy. (Right) Isselicrinidae, Metacrinus levii, synostosis. Note that this type of syzygy is difficult to distinguish from a synostosis in external view. B = basal ossicle. R = radial ossicle.

8a. (5b) At least some columnals united by synarthry; fulcral ridges of successive articulations not oriented in same plane (figure 6).
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8b. (5b) Synarthries never present in stalk.
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Fig. 6. Phrynocrinidae, Porphyrocrinus daniellalevyae, stalk columnals joined by synarthries. A. Proximal stalk. B. Middle stalk. C. Synarthrial articular facet showing transverse fulcral ridge flanked by deep semi-circular ligament fossae.

9a. (8a) Rays unbranched (figure 7A).
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9b. (8a) Ten arms only; IBr series of 2 ossicles (figure 7B).
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9c. (8a) More than 10 arms; IBr series of more than 2 ossicles (figure 7C)
---Phrynocrinidae (Phrynocrinus, Porphyrocrinus thalassae)

10a. (9a) Five unbranched arms only (figure 7A).
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10b. (9a) Up to 17 unbranched arms (figure 7D).
---Phrynocrinidae (Porphyrocrinus daniellalevyae)


Fig. 7. Arm branching patterns. A. Rhizocrinidae, Rhizocrinus lofotensis. B. Bathycrinidae, Bathycrinus complanatus.
C-D. Phrynocrinidae. C. Phrynocrinus sp. D. Porphyrocrinus daniellalevyae.

11a. (10a) Basals taller than radials; calyx ossicles with sutures visible or fused together (figure 8A-B).

11b. (10a) Radials as tall as basals or taller; calyx ossicles not fused (figure 8C-E).
---Phrynocrinidae (Porphyrocrinus spp.)


Fig. 8. A-B. Rhizocrinidae. A. Rhizocrinus cherbonnieri. B. Democrinus parfaiti. C. Phrynocrinidae, Porphyrocrinus sp. D. Caledonicrinus vaubani (family uncertain). E. Bathycrinidae, Naumachocrinus hawaiiensis. R = radial ossicle. B = basal ossicle.

12a. (9b) Basals not visible externally; calyx appears composed only of radials (figure 8D-E).
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12b. (9b) Calyx short, inverted conical; radials and basals of similar height (figure 9A-B).
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13a. (12a) Calyx swollen, much wider than top of stalk (figure 8D).
---Caledonicrinus [family assignment uncertain]

13b. (12a) Calyx tall, narrow (figure 8E).
---Bathycrinidae (Naumachocrinus)

14a. (12b) Knobby processes on interior face of IBr ossicles; proximal free arm pattern 1+2 3+4 5 or 1+2 4+5 7 (figure 9C).

14b. (12b) No knobby processes on interior face of IBr ossicles; proximal free arm pattern 1+2 3+4 7 to 1+2 3+4 9 (figure 9D).


Fig. 9. A-B. Bathycrinidae, Discolocrinus iselini. C. Bathycrinidae, Bathycrinus complanatus. D. Septocrinidae, Rouxicrinus vestitus.

15a. (8b) Calyx small, short; basals usually rounded and swollen; radials and following brachials of similar size; pinnules fragile and highly flexible (figure 10A-C).

15b. (8b) Calyx large, hollow, and thin-walled; basals fused or with irregular sutures; radials usually much larger than succeeding ossicles; pinnules well developed, rigid proximally (figure 10D-E).


Fig. 10. A-C. Guillecrinidae. A-B. Guillecrinus neocaledonicus. C. Vitjazicrinus cf. petrachenkoi. D-E. Hyocrinidae.
D. Hyocrinus bethellianus. E. Calamocrinus diomedae.

16a. (2b) Five undivided arms.
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16b. (2b) Ten or more arms.
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17a. (16a) Centrodorsal discoidal to hemispherical.
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17b. (16a) Centrodorsal conical; cirrus sockets in columns (figure 11A).

18a. (16a) First two ossicles following radials united by syzygy (br1+2); P1 on second ossicle following radial (figure 11B).

18b. (16a) First two ossicles following radials united by synarthry; P1 on second or fourth ossicle following radial (figure 11C).
---Pentametrocrinidae (Pentametrocrinus)


Fig. 11. A. Atopocrinidae, Atopocrinus ojii. B. Eudiocrinidae, Eudiocrinus venustulus. C. Pentametrocrinidae, Pentametrocrinus atlanticus.

19a. (16b) 10 or more arms arise from 10 radials.
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19b. (16b) 10 or more arms arise from 5 radials.
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20a. (19a) 10 undivided arms arising from ten radials (figure 12A).
---Pentametrocrinidae (Thaumatocrinus)

20b. (19a) 20 arms arising from ten radials (Antarctic) (figure 12B).
---“Antedonidae” (Promachocrinus)
Antedonidae now recognized as polyphyletic and requiring revision.


Fig. 12. A. Pentametrocrinidae, Thaumatocrinus jungerseni. B. “Antedonidae”, Promachocrinus kerguelensis.

21a. (19b) Distal segments of oral pinnules each bearing one or a pair of blades or teeth that together form a comb-like structure; mouth central to marginal (figure 13).
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21b. (19b) Distal segments of oral pinnules without comb-like structure; mouth always central.
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Fig. 13. Oral pinnule combs. A-D. Comatulidae. A. Alloeocomatella pectinifera. B. Comaster cf. audax. C. Oxycomanthus comanthipinnus.
D. Phanogenia typica. E. “Antedonidae”, Ctenantedon kinziei.

22a. (21a) Centrodorsal discoidal, pentagonal or stellate, thick or thin; cirri restricted to margin, sometimes few or absent; mouth usually marginal (sometimes subcentral; occasionally central); anal papilla often central or subcentral; arms 10 to >10; synarthrial tubercles absent; middle and distal pinnules often extremely spiny (figure 14 A, C-D).
---Comatulidae (formerly Comasteridae)

22b. (21a) Centrodorsal hemispheric or low conical; cirri numerous, covering most of centrodorsal; 10 arms only; synarthrial tubercles often well developed; mouth central with food grooves radiating symmetrically across tegmen (figure 14B).
(Ctenantedon kinziei - cryptic on Caribbean reefs)
(Comatonia cristata - Gulf of Mexico, Bahamas, SE U.S., to ~400m.)
(Anthrometra adriani - Antarctic & adjacent waters)

Antedonidae now recognized as polyphyletic and requiring revision.


Fig. 14. A. Comatulidae, Anneissia bennetti, oblique aboral view. B. “Antedonidae”, Anthometrina adriani, lateral view.
C-D. Comatulidae, oral surfaces. C. Clarkcomanthus littoralis, marginal mouth. D. Phanogenia typica, central mouth.

23a. (21b) Middle and distal pinnules round, oval, or flattened in cross-section (figure 15A).
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23b. (21b) Middle and distal pinnules straight, stiff, triangular in cross-section (figure 15B).
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Fig. 15. Middle pinnules. A. Mariametridae, Heterometra delagoae, round cross section. B. Thalassometridae, Cosmiometra crassicirra, triangular cross section (prismatic).

24a. (23a) Basals visible as pentagons or low interradial triangles usually forming complete circlet between centrodorsal and radials; cirrus sockets bordered by horseshoe-shaped ridge and arranged in distinct columns on conical centrodorsal; first pinnule on br10 or br12 (figure 16A-B).

24b. (23a) Basals absent or reduced to narrow rays (sometimes visible as interradial tubercles at corners of radials) or internal rosette, or both; cirrus sockets arranged in columns, spiral whorls, or irregular marginal rows, but never bordered by horseshoe-shaped ridge; P1 on br2 or br4 (figure 16C).
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Most of the following families require taxonomic revision.  Stay tuned.


Fig. 16. A-B. Atelecrinidae, illustrating complete or nearly complete basal circlet between centrodorsal and radials. A. Paratelecrinus cubensis. B. Adelatelecrinus vallatus. C. Comatulidae, Anneissia bennetti, example of reduced basal visible externally as small interradial tubercle. R = radial ossicle.

25a. (24b) IBr2 series united by syzygy (figure 17A-B).

25b. (24b) IBr2 series not united by syzygy (figure 17C-F).
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Fig. 17. A-B. Zygometridae, primibrachial articulation a syzygy (IBr2(1+2)) (arrows). A. Zygometra comata. B. Zygometra microdiscus, syzygy less recognizable. C-F. Primibrachial articulation a synarthry; arrows indicate where ends of fulcral ridges of the two ossicles abut midaborally. C-D. Comatulidae. C. Comaster schlegelii, primibrachial articulation a close synarthry or “cryptosynarthry”. D. Comactinia meridionalis. E. “Antedonidae”, Hybometra senta, primibrachial articulation with strong projecting synarthrial tubercle. F. Charitometridae, Crinometra brevipinna.

26a. (25b) At least some middle and/or distal cirrus segments with a pair of side-by side aboral tubercles or spines; sometimes one or two transverse ridges (figure 18A-D).

26b. (25b) Aboral surface of middle and distal cirrus segments smooth or with spine, keel or median tubercle (figure 18E-H).
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Fig. 18. Aboral cirral ornamentation. A-D. Colobometridae. A. Analcidometra armata, paired flanking spines with central spine. B. Iconometra cf. anisa, curved transverse ridges. C. Decametra tigrina, short transverse ridge on middle cirrals reduced to midaboral spine on distal cirrals. D. Colobometra perspinosa, paired spines. E. Mariametridae, Dichrometra cf. palmata, aboral carina/keel. F. Thalassometridae, Horaeometra duplex, sharp aboral spines. G. Comatulidae, Neocomatella pulchella, blunt aboral spines/tubercles. H. “Antedonidae”, Comatonia cristata, no aboral ornamentation (except opposing spine).

27a. (26b) Gonads on arms at pinnule bases; 10 arms only; Antarctic and adjacent waters (figure 19A-B).

27b. (26b) Gonads on pinnules; 10 or more arms (figure 19C-F).
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Fig. 19. A-B. Notocrinidae, Notocrinus virilis, gonad at base of genital pinnule. C-F. Gonad along genital pinnule. C-E. “Antedonidae”. C. Phrixometra longipinna. D. Kempometra grisea. E. Dorometra parvicirra. F. Charitometridae, Poecilometra acoela, 3rd or 4th to 6th pinnular expanded over gonad, which is covered with ambulacral plates. G = gonad.

28a. (27b) Arms no more than 30 mm long; second arm syzygy proximal to br9+10; genital pinnules with both gonads and marsupia for brooded larvae; aboral surface of distal cirrals flattened; southern Australia (figure 20A-B).

28b. (27b) Arms ranging from <30 to over 200 mm long; second arm syzygy at or distal to br9+10; no marsupia; aboral surface of cirrals not flattened; tropical shallow to deep sea (figure 20C).
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Fig. 20. A-B. Aporometridae, second syzygy proximal to br9+10. A. Aporometra wilsoni. B. Aporometra occidentalis. C. “Antedonidae”, Poliometra prolixa, second syzygy at br9+10.

29a. (28b) Cirrus sockets with deep concave fulcral bowl surrounding central lumen; basals visible externally as pentagonal extension of centrodorsal radial ridges, sometimes forming narrow strip in deep subradial clefts; centrodorsal chiefly taller than wide, sometimes dome-shaped (figure 21A).

29b. (28b) Cirrus sockets shallow, never with deep fulcral bowl; basals reduced to narrow rays or internal rosette; centrodorsal widely variable, from disc-like to tall and conical (figure 21B).
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Fig. 21. A. Zenometridae, Psathyrometra sp., cirrus sockets with deep bowl. B. Mariametridae, Dichrometra bimaculata, sockets lacking deep bowl.

30a. (29b) Ten arms only; second syzygy at br9+10; distal interval between syzygies usually 2-4 (infrequently longer).
Antedonidae now recognized as polyphyletic and requiring revision.

30b. (29b) Chiefly ten arms only; second syzygy usually at br9+10; distal interval between syzygies usually 6 or greater (often >10).
---Himerometridae (Amphimetra)

30c. (29b) More than ten arms (except in very small specimens); second syzygy usually distal to br9+10; distal interval usually 5 or greater (often >10).
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31a. (30c) IIBr and following brachitaxes (=division series) of 2 ossicles only (figure 22A).

31b. (30c) IIBr4(3+4) (rarely 2), following brachitaxes (=division series) 2 or 4(3+4) (figure 22B).


Fig. 22. A. Mariametridae, Dichrometra brachypecha, brachitaxes of 2 ossicles. B. Himerometridae, Himerometra robustipinna, brachitaxes 4(3+4).

32a. (23b) 10 arms only; pinnules with microscopic ambulacral covering plates sometimes present; cirri stout; cirrals without aboral ornament.

32b. (23b) 10 or more arms; pinnules with conspicuous ambulacral covering plates; cirrals with or without aboral spine, keel, or tubercle (figure 23).
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Fig. 23. Pinnules with well-developed ambulacral (side and covering) plates.

33a. (32b) P1 delicate and weak, but with the first two segments greatly enlarged; disk globose, covered with a pavement of plates, and easily detached (figure 24A).

33b. (32b) P1 not especially delicate or weak; first two segments not greatly enlarged; disk usually stellate; disk plates or nodules not forming pavement (figure 24B).
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Fig. 24. First pinnule (P1). A. Calometridae, Calometra discoidea with greatly enlarged first two pinnulars. B. Thalassometridae, Thalassometra sp.

34a. (33b) Cirri usually short and stout, usually of <25 segments, <20% of arm length, and without aboral spines (at most a blunt tubercle) (figure 25A-B).

34b. (33b) Cirri slender and usually strongly prehensile, usually long and of at least 30 segments (often >50); distal cirrals usually with aboral keel or spine (figure 25C).
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Fig. 25. Cirri. A-B. Charitometridae. A. Crinometra brevipinna. B. Poecilometra acoela. C. Thalassometridae, Cosmiometra iole.

35a. (34b) P1 longer and stouter than P2.

35b. (34b) P1 shorter and slenderer than P2.
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36a. (35b) Muscular fossae on radials extremely short; centrodorsal columnar; cirri in 15-20 crowded irregular columns; southern Australia (figure 26A).

36b. (35b) Muscular fossae on radials at least as tall as wide; centrodorsal short, columnar but with a conical pole; cirri arranged in ten distinct columns; East Indies to Japan (figure 26B).


Fig. 26. Centrodorsal and radial pentagon, lateral views. A. Ptilometridae, Ptilometra australis. B. Asterometridae, Asterometra macropoda.


Agassiz, A. (1890) Notice of Calamocrinus diomedae, a new stalked crinoid from the Galapagos, dredged by the U.S. Fish Commission Steamer “Albatross.” Bulletin of the Museum of Comparative Zoology, Harvard 20(6):165–167.

Carpenter, P. H. (1884). Report on the Crinoidea collected during the voyage of H.M.S. Challenger, during the years 1873-1876. Part I. The Stalked Crinoids. Report on the Scientific Results of the Voyage of H.M.S. Challenger during the years 1873–76. Zoology. 11 (part 32):i-xii, 1-442, pl. 1-62.

Clark, A. H. (1921). A monograph of the existing crinoids, Vol. 1, The comatulids, Pt. 2. Bulletin of the United States National Museum 82:i-xxv, 1-795, 57 pls.

Clark, A. M. (1972) Some crinoids from the Indian Ocean. Bulletin of the British Museum of Natural History (Zoology) 24(2):73-156.

Meyer, D. L. (1972) Ctenantedon, a new antedonid crinoid convergent with comasterids. Bulletin of Marine Science 22:53–66.

Mironov, A. N. (2008). Stalked crinoids of the family Bathycrinidae (Echinodermata) from the eastern Pacific. Invertebrate Zoology 5(2):133-153.

Mironov, A. N. & Pawson, D. L. (2010). A new genus and species of Western Atlantic sea lily in the family Septocrinidae (Echinodermata: Crinoidea: Bourgueticrinida). Zootaxa 2449(1):49-68.

The following illustrations were originally drawn by C. G. Messing for the following:

Messing, C. G. (1975) The systematics and distribution of the Crinoidea Comatulida (exclusive of Macrophreatina) collected by the R/V GERDA in the Straits of Florida and adjacent waters. M.S. Thesis, University of Miami, 285 pp. Figures 17D, F, 18F, G.

Messing, C.G. (1978) Pentametrocrinus atlanticus (Perrier) (Echinodermata: Crinoidea): A review. Journal of Natural History 12:699-708. Figure 11C.

Messing, C. G. (1981) Reclassification and redescription of the comatulid Comatonia cristata (Hartlaub) (Echinodermata: Crinoidea). Proceedings of the Biological Society of Washington 94:240-253. Figure 18H.

Messing, C. G. (2001) A key to the genera of Comasteridae (Echinodermata: Crinoidea) with the description of a new genus. Bulletin of the Biological Society of Washington 10:277-300. Figures 14C, D.

Messing, C. G. (2013) A revision of the genus Atelecrinus PH Carpenter (Echinodermata: Crinoidea) Zootaxa 3681 (1): 001–043. Figures 16A, B.

Messing, C. G. & Dearborn, J. (1990) Marine Flora and Fauna of the northeastern United States. Echinodermata:Crinoidea. NOAA Technical Report, National Marine Fisheries Service No. 91, 33 pp. Figure 7A.

Roux, M., Messing, C. G. & Améziane, N. (2002) Artificial keys to the genera of living stalked crinoids (Echinodermata). Bulletin of Marine Science 70(3):799-830. Figures 3C, 5A-C, 8A-B, D-E, 10A.

The following illustration was drawn by Dana Rankin for:

Rankin, D.L. & Messing, C. G. (2008) A revision of the comatulid genus Stephanometra A.H. Clark with a rediagnosis of the genus Lamprometra A.H. Clark (Echinodermata: Crinoidea). Zootaxa 1888:1-35. Figure 18E.